Large sized motor vehicle with high weight capacities, e.g. buses and tractor-trailers include multiple pairs of wheels on the vehicle's rear axle(s). This is required to support and uniformly distribute the vehicle weight on the road surface. Commonly referred to as "dual wheel" vehicles (actually dual wheel pairs) they include vehicles with at least one rear axle having at least one pair of wheels on either end of the axle.
A known characteristic of dual wheel vehicles is that underinflated or deflated tires within a wheel pair do not give a visual appearance of being flat since the remaining inflated tires on the axle fully support the vehicle weight. As a result, the vehicle axle is maintained at the same distance above the roadway surface by the remaining inflated tires. The underinflated tire does not carry any of the load and, therefore, does not sag or crush to the pavement. Flat tires are simply not visible as they are on single wheel axles, resulting in ultimate tire failure on the highway.
Absent the ability to visually detect underinflated tires, the obvious solution is to frequently measure actual tire pressure. However, as known to dual wheel vehicle operators and maintenance personnel, there is no easy way to quickly and accurately measure the tire pressure of the inboard wheel of a dual wheel pair, i.e. the tire mounted on the wheel closest to the vehicle chassis. Although measurement of the inboard tire pressure is possible with effort, it is difficult enough to discourage frequent measurement. The result is that most often actual tire pressure measurement is made only during scheduled maintenance of the vehicle. An alternate, but less quantitative method used by vehicle operators includes striking the tire with some type of club or iron, and judging by the feel and sound whether or not the tire is inflated. This method is accurate only for gross failures, i.e. flat tires, since it depends on the experience and judgment of the person performing the test. An underinflated tire may feel inflated, but may still be sufficiently smaller in diameter than the mating tire so as to scuff along the roadway surface. This scuffing abraids the tire resulting in heat build-up and tire blow out or fire. All of which could be avoided by frequent tire pressure measurement.